In what organisms does anaerobic respiration primarily occur?

Anaerobic respiration primarily occurs in bacteria and yeast, which are capable of generating energy without the use of oxygen. In these organisms, anaerobic processes allow them to live in environments where oxygen is scarce or absent. For instance, yeast perform fermentation to produce ethanol and carbon dioxide when oxygen is not available, which is crucial for making bread and alcoholic beverages. Similarly, certain bacteria engage in various fermentation pathways or convert compounds like sulfate or nitrate instead of oxygen to obtain energy.

In contrast, humans and mammals primarily rely on aerobic respiration, using oxygen to efficiently produce energy. Although certain conditions, like intense exercise, can lead to anaerobic respiration in human muscles (producing lactic acid), it is not the primary mode of energy production.

Plants, while capable of both aerobic and anaerobic respiration, primarily use aerobic pathways when sufficient light and oxygen are available for photosynthesis.

Aquatic animals generally rely on aerobic respiration as well, utilizing the oxygen dissolved in water. Therefore, the unique capabilities of bacteria and yeast for anaerobic respiration set them apart as the primary organisms where this process occurs.